全文获取类型
收费全文 | 254篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
化学 | 192篇 |
晶体学 | 1篇 |
数学 | 34篇 |
物理学 | 35篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 7篇 |
2015年 | 4篇 |
2014年 | 10篇 |
2013年 | 11篇 |
2012年 | 13篇 |
2011年 | 9篇 |
2010年 | 22篇 |
2009年 | 13篇 |
2008年 | 24篇 |
2007年 | 14篇 |
2006年 | 13篇 |
2005年 | 9篇 |
2004年 | 12篇 |
2003年 | 12篇 |
2002年 | 11篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有262条查询结果,搜索用时 15 毫秒
61.
Jairo Quiroga Angelina Hormaza Braulio Insuasty Manuel Mrquez 《Journal of heterocyclic chemistry》1998,35(2):409-412
A series of dihydropyrazolo[3,4-b]pyridin-6-ones 3 was prepared by cyclization of 5-amino-1-aryl-3-methylpyrazoles 1 and Meldrum's acid benzylidene derivatives 2 in nitrobenzene. The structure of 4,5-dihydropyrazolo[3,4-b]pyridin-6-ones and reaction orientation were determined by nmr measurements. 相似文献
62.
Carmona D Sáez J Granados H Pérez E Blair S Angulo A Figadere B 《Natural product research》2003,17(4):275-280
Dichloromethane extracts of both the roots and the leaves of Raimondia cf. monoica showed in vitro antiplasmodial and leishmanicidal activities against Plasmodium falciparum and Leishmania panamensis, respectively. Three 6-substituted 5,6-dihydro-2H-pyran-2-ones were isolated. (1) and (2) were identified as (6S)-(5'-oxohepten-1'E,3'E-dienyl)-5,6-dihydro-2H-pyran-2-one (1) and (6R)-(5'-oxohepten-1'Z,3'E-dienyl)-5,6-dihydro-2H-pyran-2-one (2), respectively. (-)-Arentilactone (3) was also isolated. The structure of the new compound (1) was determined by spectroscopic methods; additional spectroscopic data for (2) are reported for the first time. 相似文献
63.
Adolfo Ensuncho M. Jennifer Lafont Alexandra Rotinov Rosa M. Domínguez Armando Herize Gabriel Chuchani Jairo Quijano 《国际化学动力学杂志》2001,33(8):465-471
The gas‐phase elimination kinetics of the ethyl ester of two α‐amino acid type of molecules have been determined over the temperature range of 360–430°C and pressure range of 26–86 Torr. The reactions, in a static reaction system, are homogeneous and unimolecular and obey a first‐order rate law. The rate coefficients are given by the following equations. For N,N‐dimethylglycine ethyl ester: log k1(s?1) = (13.01 ± 3.70) ? (202.3 ± 0.3)kJ mol?1 (2.303 RT)?1 For ethyl 1‐piperidineacetate: log k1(s?1) = (12.91 ± 0.31) ? (204.4 ± 0.1)kJ mol?1 (2.303 RT)?1 The decompositon of these esters leads to the formation of the corresponding α‐amino acid type of compound and ethylene. However, the amino acid intermediate, under the condition of the experiments, undergoes an extremely rapid decarboxylation process. Attempts to pyrolyze pure N,N‐dimethylglycine, which is the intermediate of dimethylglycine ethyl ester pyrolysis, was possible at only two temperatures, 300 and 310°C. The products are trimethylamine and CO2. Assuming log A = 13.0 for a five‐centered cyclic transition‐state type of mechanism in gas‐phase reactions, it gives the following expression: log k1(s?1) = (13.0) ? (176.6)kJ mol?1 (2.303 RT)?1. The mechanism of these α‐amino acids differs from the decarbonylation elimination of 2‐substituted halo, hydroxy, alkoxy, phenoxy, and acetoxy carboxylic acids in the gas phase. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33:465–471, 2001 相似文献
64.
Debora Cobo Jairo Quiroga Justo Cobo Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(9):o444-o446
The title compound, C14H11NS, crystallizes with Z′ = 0.75 in the space group C2/m. Two independent molecules are present, one of which lies with all the non‐H atoms on a mirror plane, while the other is fourfold disordered across a site of 2/m symmetry. The ordered molecules are stacked such that they enclose continuous channels running along twofold rotation axes, and the disordered molecules are positioned within these channels. 相似文献
65.
Jairo Quiroga Carlos Cisneros Braulio Insuasty Rodrigo Abonía Manuel Nogueras Maximiliano Sortino Susana Zacchino 《Journal of heterocyclic chemistry》2006,43(2):463-469
The free‐solvent multicomponent reaction under microwave irradiation of 6‐aminopyrimidin‐4(3H)‐ones ( 1 ) with dimedone ( 2 ) and N,N‐dimethylformamide dimethylacetal yields the pyrimido[4,5‐c]isoquinolinones ( 5a‐j ). In this process, the intermediate of cyclization was isolated. The structure of the synthesized compounds was determined on the basis of nmr measurements, especially by 1H,1H‐,1H,13C COSY, and DEPT. These compounds showed antifungal in vitro activity particularly against dermatophytes. 相似文献
66.
Jairo Bordinhão Glaucio B. Ferreira Carolina X.A. da Silva 《Journal of organometallic chemistry》2006,691(8):1598-1605
The synthesis and crystal structures of 4,5-bis[(triorganotin)thiolato]-1,3-dithiole-2-thione, (R3Sn)2(dmit), 1, and 4,5-bis[(triorganotin)thiolato]-1,3-dithiole-2-one, (R3Sn)2(dmio), 2, compounds are reported. Compounds, (1 or 2: R = Ph or cyclohexyl, Cy), have been obtained from reaction of R3SnCl with Cs2dmit or Na2dmio. The presence of the two tin centres in (2: R = Ph) is shown in the 13C NMR spectrum by the couplings of both Sn atoms to the dmio olefinic carbons with J values of 29.4 and 24.7 Hz. The δ119 Sn values for (1: R = Ph) and (2: R = Ph) differ by about 30 ppm, values being −20.7 and −50.1 ppm, respectively, in CDCl3 solution. X-ray structure determinations for (1: R = Ph) and (2: R = Ph or Cy) reveal the compounds to have 4-coordinate, distorted tetrahedral tin centres. The dithiolato ligands, dmit and dmio, act as bridging ligands, in contrast to their chelating roles in R2Sn(dmit) and R2Sn(dmio). A further difference between R2Sn(dmit) and R2Sn(dmio), on one hand, and 1 and 2 on the other, is that intermolecular Sn-S and Sn-O interactions are absent in 1 and 2. However, weak intermolecular hydrogen bonding interactions are found in (1: R = Ph) [C-H?π] and in (2: R = Ph) [C-H?π and C-H?O]. 相似文献
67.
Heleno VC da Silva R Pedersoli S de Albuquerque S Bastos JK Silva ML Donate PM da Silva GV Lopes JL 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,63(1):234-239
In this paper we present a complete 1H and 13C NMR spectral analysis of three lignan lactones (methylpluviatolide, dimethylmatairesinol and hinokinin) by the use of techniques such as COSY, HMQC, HMBC and J-resolved. Complete assignment and all homonuclear hydrogen coupling constant measurements were performed, providing enough data also to the confirmation of the relative stereochemistry. 相似文献
68.
We show that a stably ergodic diffeomorphism can be approximated by a diffeomorphism having stably non-zero Lyapunov exponents. To cite this article: J. Bochi et al., C. R. Acad. Sci. Paris, Ser. I 342 (2006). 相似文献
69.
Yurina Díaz Jairo Quiroga Justo Cobo Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(3):o137-o140
The molecules of the title compound, C26H19Cl2N5, are conformationally chiral, with none of the aryl groups coplanar with the pyrazolo[3,4‐b]pyridine core of the molecule. A single unique N—H...N hydrogen bond links the molecules into two symmetry‐related sets of C(11) chains running parallel to the [011] and [01] directions, respectively, and these two sets of chains are linked into a continuous three‐dimensional framework structure by a single unique C—H...N hydrogen bond which forms a chain parallel to the [100] direction. 相似文献
70.
5-Methoxy-3H-naphtho[2,1,8-mna]xanthen-3-one (musafluorone, 1), the only naphthoxanthenone reported so far from Musaceae, was synthesized starting from 2-naphthol in nine steps and resulted in an overall yield of 3%. Grignard addition of phenylmagnesium bromide to 4-methoxyperinaphthenone afforded the corresponding 4-methoxy-9-phenylphenalenone which, after epoxidation and methyl transposition, was subjected to a photochemical cyclization procedure to furnish 1. 相似文献